The continued scaling down of semiconductor devices features and thin films makes the high resolution scanning electron microscope (SEM) a necessary analytical tool for examining surface structures and interfaces. The SEM makes it possible to view much smaller areas on semiconductor devices than is possible with other types of microscopes or viewing equipment. To see many of these areas, it is necessary to cut or slice sample semiconductor devices. As devices are cut using known techniques, however, damage to the semiconductor device may occur. As microstructures continue to gain importance in the semiconductor industry, the adverse effects of manual cleaving or cutting to obtain SEM specimens become even more pronounced. Since more and more circuits are using these sub-micron devices, the utility of manual cleaving procedures has diminished significantly.
In today's semiconductor industry, minimizing process time and improving product quality are dominant obsessions. For example, a primary goal for failure analysis laboratories is rapid and accurate analysis of component failures to find the root cause of process problems. Most notable among improved failure analysis equipments is a lapping equipment, such as that for accomplishing the technique detailed in T. Mills & E. W. Sonheimer, "Precision VLSI Cross-Sectioning and Staining," 1982 Int'l Reliability Phys. Symp., 20th Ann'l Proc., pp. 214-220, IEEE, New York, N.Y., and B. R. Hammond & T. R. Vogel, "Non-Encapsulated Microsectioning as a Construction and Failure Analysis Technique," 1982 Int'l. Reliability Phys. Symp. 20th Ann'l Proc., pp. 221-223, IEEE, New York, N.Y. This lapping equipment delicately grinds the semiconductor device using a diamond wheel similar to that used to cut or polish glass and jewels. Using a precision lapping tool enables cross-sectioning at a .+-.0.2 micron scale with a 90% competence level of the depth and location of lapping.
The precision lapping technique places the SEM specimen in contact with a rotating diamond wheel under running water (DI or city water) at a speed of approximately 200 rpm. Using this improved lapping technique, however, damage to the semiconductor devices may still occur. For example, often it has been shown that deformation and scratches of the semiconductor device may occur from the lapping procedure. Deformation and scratches are principally due to particulates chipping away from the semiconductor device and adhering to the polishing surface. These particulates rotate back with the lapping wheel to cause damage to the semiconductor device itself. The complications of deformations and scratches slow the failure analysis process by causing the process to take longer and be less accurate.
Fine polishing of the semiconductor specimens in the lapping equipment can also cause particulate to build up at an edge of the semiconductor specimen as a result of the rotating lapping wheel carrying with it particulate that is polished or chipped away from the semiconductor device. This buildup makes it difficult to precisely cross-section the semiconductor devices at desired locations. This is due to crushed materials that accumulate on the front side of the lap specimen. These crushed materials get in the way of the lapping wheel surface and significantly affect cutting the SEM specimen.
There is a need, therefore, for an improved semiconductor device precision lapping technique that avoids the deformation and scratches associated with known cleaning and lapping techniques.
There is a need for a method and system for semiconductor structure precision lapping that permit precise cross-sectioning of the semiconductor structure at required locations and avoid the accumulation of crushed materials over the front side of the lapped specimen.
Further, there is a need for a semiconductor structure lapping method and apparatus that permit more rapid and effective lapping of semiconductor devices and overcome the need to continually rework and relap semiconductor devices during SEM analysis.